Surface-emitting laser elements (or vertical cavity surface-emitting laser elements—VCSELs) are characterized in that laser light can be emitted in a perpendicular direction to the principal surface of a substrate formed with the element and in that the element has low threshold current and high power conversion efficiency. In addition, surface-emitting laser elements have various advantages, for example, that they emit circular light whose cross-section perpendicular to the optical axis is circular, that two-dimensional arrangement of them is facilitated, and that on-wafer inspection of them can be carried out efficiently. A VCSEL is suitable for use as the light source in various consumer applications including, for example, an image forming apparatus, an optical pickup device, the optical communication data transmitter of optical interconnections and optical modules, etc. Optical modules made with VCSELs also have applications in high-speed data transmission. At least in part due to such advantages, it is expected that the demand for surface-emitting laser elements as light sources for high-speed data communications will increase in the future.
In using a surface-emitting laser element for a light source for high speed data communication applications, it is generally desirable for the element to have a structure optimized for operating at high speed. In order for the surface-emitting laser element to accomplish a high-speed operation 10-40 Gbit/s and above, for example, it is especially desirable to optimize or otherwise improve characteristics of the optical transmission source such as control of photon lifetime, control of photon relaxation oscillation damping behavior and filtering of transverse optical modes that contribute to achieving an optimal and stable dynamic performance of a laser.
Certain example embodiments, as described below, help address these and/or other aspects.
Some embodiments provide an optical phase element that controls photon lifetime & relaxation oscillation damping behavior and filters transverse optical modes for best dynamic performance of a laser for high-speed data-transfer applications. Some embodiments include semiconductor lasers, such as VCSELs at 850 nm emission wavelength, integrated with tunable optical phase filters as reliable optical transmitters that have high potential in high-speed data communication for short reach applications.
An example embodiment provides a 850 nm VCSEL transmitter which includes an active region having one or more quantum wells having InGaAs material and two or more quantum well barriers having AlGaAs or GaAsP materials adjacent to the one or more quantum wells. A surface relief structure is made on either i) the topmost GaAs surface/contact layers by either dry or wet etching or ii) with the help of PECVD made thin SiN layer made on GaAs layer with wet etching for tunable static and dynamic characteristics such as output power, slope efficiency, and resonance oscillation bandwidth, photon lifetime through its damping, rise/fall times of eye-opening, over shooting, and jitter respectively.
According to an example embodiment, a vertical cavity surface-emitting laser element (VCSEL) comprises a top distributed Bragg reflector (DBR) and a bottom DBR each made with multiple layers of semiconductor thin films, an active region having at least one quantum well and at least one quantum well barrier each having a thickness of 3-10 nm formed between the top DBR and the bottom DBR, and a surface relief structure formed on at least the top-most layer of the top DBR by dry or wet etching of semiconductor or dielectric thin films. The at least one quantum well comprises InGaAs with an In proportion of 0.04-0.12, the at least one quantum well barrier comprises AlxGaAs where x is between 0.3-0.4 or GaAsPy where y is between 0.2-0.3, and the at least one quantum well is adjusted for a photoluminescence emission target between 835-840 nm. The surface relief structure has a depth of 20-150 nm and a diameter of 2-6 um, and the top surface of the top-most layer is terminated (1) either in-phase or anti-phase in relation to a standing wave corresponding to the VCSEL, and/or (2) in a layer having a fixed thickness in between the anti-phase and in-phase condition of the standing wave.
According to an example embodiment, a VCSEL comprises a top DBR and a bottom DBR each made with multiple layers of semiconductor thin films, an active region having at least one quantum well and at least one quantum well barrier each having a thickness of 3-10 nm formed between the top DBR and the bottom DBR, and a semiconductor step or ring surface relief structure having a depth of 20-50 nm and a diameter of 2-6 um formed on at least one top most layers of the top DBR. The at least one quantum well comprises InGaAs with an In composition of 0.04-0.12, the at least one quantum well barrier comprises AlxGaAs where x is between 0.3-0.4 or GaAsPy where y is between 0.2-0.3, and the at least one quantum well is adjusted for a photoluminescence emission target between 835-840 nm. The top most layer may be p-doped, and is terminated (1) either in-phase or anti-phase in relation to a standing wave corresponding the VCSEL, and/or (2) in a layer having a fixed thickness in between the anti-phase and in-phase condition of the standing wave.
According to an example embodiment, a VCSEL comprises a top DBR and a bottom DBR each made with multiple layers of semiconductor thin films, an active region having at least one quantum well and at least one quantum well barrier each having a thickness of 3-10 nm formed between the top DBR and the bottom DBR, and a dielectric step or ring surface relief structure having a depth of 20-150 nm and a diameter of 2-6 um formed on at least one top-most layer of the top DBR. The at least one quantum well comprises InGaAs with an In proportion of 0.04-0.12, the at least one quantum well barrier comprises AlxGaAs where x is between 0.3-0.4 or GaAsPy where y is between 0.2-0.3, and the at least one quantum well is adjusted for a photoluminescence emission target between 835-840 nm. The top-most layer may be p-doped. The surface relief structure is formed by wet chemical etching of dielectric layers fabricated on the at least one top-most layer, and the top-most dielectric layer is terminated (1) either in-phase or anti-phase in relation to a standing wave corresponding the VCSEL, and/or (2) in a layer having a fixed thickness in between the anti-phase and in-phase condition of the standing wave.
Some example embodiments include the above VCSELs wherein the emission wavelength is in the wavelength range of 850-860 nm. The VCSELs may include both anode and cathode electrical contacts arranged as top-top configuration. The VCSEL may be grown on p-doped or n-doped or un-doped (semi-insulating) GaAs substrate.
The VCSELs may further comprise at least one AlxGa1−xAs oxidation layer with Al content of at least 98 percent, and when multiple oxide layers are available, forming at least one oxide layer placed above and below optical cavity/gain region of the VCSEL. The VCSEL may further comprise mesa passivation with low dielectric constant materials such as one or more of SiN and BCB.
Some example embodiments include VCSEL in which the surface relief structure is formed on the top-most layer and one or more layers consecutively below the top-most layer, wherein the layers in which the surface relief is formed includes one or more of P++GaAs contact, AlGaAs GIRN, or Al0.12GaAs layers.
Some example embodiments include VCSEL in which the dry etching includes inductively coupled plasma reactive ion etching (ICP-RIE).
Some example embodiments include VCSEL in which the dielectric layer comprises SiN.
Another example embodiment provides a method of manufacturing a VCSEL. The method comprises: forming a top distributed Bragg reflector (DBR), a bottom DBR and an active region, wherein the top and bottom DBRs each being with multiple layers of semiconductor thin films, and wherein the active region having at least one quantum well and at least one quantum well barrier each having a thickness of 3-10 nm formed between the top DBR and the bottom DBR; and forming a surface relief structure formed on at least the top-most layer of the top DBR by dry or wet etching of semiconductor or dielectric thin films, wherein the surface relief structure has a depth of 20-150 nm and a diameter of 2-6 um, and the top surface of the top-most layer is terminated (1) either in-phase or anti-phase in relation to a standing wave corresponding the VCSEL, and/or (2) in a layer having a fixed thickness in between the anti-phase and in-phase condition of the standing wave. The at least one quantum well comprises InGaAs with an In proportion of 0.04-0.12, the at least one quantum well barrier comprises AlxGaAs where x is between 0.3-0.4 or GaAsPy where y is between 0.2-0.3, wherein the at least one quantum well is adjusted for a photoluminescence emission target between 835-840 nm.
Another example embodiment provides a method of manufacturing a VCSEL. The method comprises: forming a top distributed Bragg reflector (DBR), a bottom DBR and an active region, wherein the top and bottom DBRs each being with multiple layers of semiconductor thin films, and wherein the active region having at least one quantum well and at least one quantum well barrier each having a thickness of 3-10 nm formed between the top DBR and the bottom DBR; and forming a semiconductor step or ring surface relief structure having a depth of 20-50 nm and a diameter of 2-6 um formed on at least one top most layers of the top DBR, the top most layer being p-doped, and wherein the top-most layer is terminated (1) either in-phase or anti-phase in relation to a standing wave corresponding the VCSEL, and/or (2) in a layer having a fixed thickness in between the anti-phase and in-phase condition of the standing wave. The at least one quantum well comprises InGaAs with an In proportion of 0.04-0.12, the at least one quantum well barrier comprises AlxGaAs where x is between 0.3-0.4 or GaAsPy where y is between 0.2-0.3, wherein the at least one quantum well is adjusted for a photoluminescence emission target between 835-840 nm.
Another example embodiment provides a method of manufacturing a VCSEL. The method comprises: forming a top distributed Bragg reflector (DBR), a bottom DBR and an active region, wherein the top and bottom DBRs each being with multiple layers of semiconductor thin films, and wherein the active region having at least one quantum well and at least one quantum well barrier each having a thickness of 3-10 nm formed between the top DBR and the bottom DBR; and forming a dielectric step or ring surface relief structure having a depth of 20-150 nm and a diameter of 2-6 um on at least one top-most layer of the top DBR, the top-most layer being p-doped, wherein the surface relief structure is formed by wet chemical etching of dielectric layers fabricated on the at least one top-most layer, and wherein the top-most dielectric layer is terminated (1) either in-phase or anti-phase in relation to a standing wave corresponding the VCSEL, and/or (2) in a layer having a fixed thickness in between the anti-phase and in-phase condition of the standing wave. The at least one quantum well comprises InGaAs with an In composition of 0.04-0.12, the at least one quantum well barrier comprises AlxGaAs where x is between 0.3-0.4 or GaAsPy where y is between 0.2-0.3, wherein the at least one quantum well is adjusted for a photoluminescence emission target between 835-840 nm.
These aspects, features, and example embodiments may be used separately and/or applied in various combinations to achieve yet further embodiments of this invention.